Annulus fillers span the radially inner aerodynamic annulus gap between fan or compressor blades. The width of the annulus gap varies during engine operation because of blade vibrations, relative movement of adjacent blades and twisting of blades. Thus the annulus filler is required to fill a varying width between blades.
An annulus filler is a weight-efficient solution rather than forming the annulus line using an integral part of a disc and can offer better sealing. Current annulus fillers used on the Applicant's Trent® series of engine fillers are machined aluminium alloy forging. The annulus filler is self-loading and as a rotating component, the majority of the forces during running are generated by its own mass. A lighter weight annulus filler would thus reduce its own internal forces, and reduce forces on the fan disc. A secondary benefit in reducing the mass of these components is to reduce the weight of the engine module. This will contribute to improved efficiency of the aircraft.
There are numerous annulus filler designs in use today and most are attached to the disc via pins, dovetail joints or hook arrangements to engage the blade or disc or both. These arrangements require dedicated features on the disc, which being a critical part, necessitates special design and manufacturing control. Furthermore, these fixtures and features are prone to wear and/or fretting fatigue that is clearly highly undesirable for a critical part. These conventional arrangements require also separate compliant seals between the annulus fillers and blades and these seals are notoriously difficult to secure and often fail in service.